Lúrio Waterfalls, Chiúre

A(i)Site contains one or more globally threatened species

The Lúrio Waterfalls qualify as an IPA under criterion A(i) as this site contains the entire known population of Aloe argentifolia, which is assessed as globally Vulnerable (VU D1) due to its extremely small population size and distribution (Martínez-Richart et al. 2019).

The Quedas do Rio Lúrio, or Lúrio Waterfalls, are a dramatic series of waterfalls and rapids at the head of a gorge on the Lúrio River approximately 70 km upstream from the mouth of the river. The Lúrio is one of the major rivers of northern Mozambique flowing for over 500 km west to east before reaching the Indian Ocean south of Mecufi. It forms the border between Nampula Province to the south and Cabo Delgado and (further upstream) Niassa Provinces to the north. The falls can be approached from the Cabo Delgado (Chiúre District) side, via an unpaved road from near Najane. The river drops from an elevation of approximately 160 m above the falls to 120 m in the gorge, with a series of large, exposed rock outcrops between the falls that support a well-developed succulent vegetation including the only known population globally of Aloe argentifolia.

The Lúrio Waterfalls are of global importance as the only known locality for the striking rosette-forming shrub aloe, Aloe argentifolia. A large population of this species, estimated at between 300 and 500 mature individuals, is known from the head of the river gorge (Martínez-Richart et al. 2019). Despite extensive surveys of aloe diversity in Mozambique in recent years, no other populations of A. argentifolia have been located and it appears that it is a very narrow endemic, confined to this unique locality created by the waterfall system (McCoy et al. 2017).
This site is otherwise not well known botanically and may well contain other species of interest. The falls are difficult to access during the main rainy season because of impassable roads and high water level of the Lúrio, hence to our knowledge, it has never been botanised at that time. It would be desirable to conduct a general botanical inventory, focusing on the succulent flora on the exposed rock outcrops and investigating the possibility of a rheophytic flora associated with the waterfalls.

The principle habitat of interest is the rocky outcrops between the waterfalls and rapids. During the rainy season these rocks receive substantial mist-spray from the adjacent falls but during the dry season the water levels are low and the rocks rapidly dry out, hence supporting a drought-tolerant flora including succulent species. McCoy et al. (2017) noted that Aloe argentifolia grows in association with the terrestrial orchid Eulophia petersii, and with species of Commiphora, Cynanchum, Kalanchoe, Sansevieria (= Dracaena) and a large caespitose Xerophtya species. Botanical collections made here in 1948 by E.C. Andrada recorded the localised Millettia bussei (LC; Andrada #1280) among the woody flora, with Adansonia digitata and Sterculia and Acacia spp. also noted in the dry woodland. The waterfalls themselves may provide habitat for rheophytic plant species; this requires further investigation.
Average rainfall is estimated at 1,487 mm per year at the nearby town of Namapa, with a marked peak in December to March and a prolonged dry season in May to October (worldweatheronline.com), resulting in the marked seasonal changes in water level on the Lúrio as noted above.

The Lúrio Waterfalls are not currently protected. However, threats appear to be minimal at present. The site is quite isolated and inaccessible for parts of the year, offering some protection for the natural vegetation. Further, the rock outcrops with thin soils are not impacted by agricultural activity or fire. The site may in future become an ecotourist destination due to its natural beauty, but as it is so isolated it is unlikely to ever receive significant tourist pressure (T. Rulkens pers. obs.).
The future integrity of the site is less certain. There are plans to construct a major hydroelectric plant on the Lúrio River to supply electricity to Cabo Delgado and Nampula Provinces (Macauhub 2014; McCoy et al. 2017). Whilst the proposed locality for this plant is understood to be a considerable distance upriver from the waterfalls, the hydroelectric dam could significantly alter downstream flow and this could impact the ecology of the waterfalls site, particularly through reducing amounts of mist-spray onto the rock outcrops from the falls during the wet season. It is unclear as to how reliant the aloe population is on the river as a moisture source.
A more pressing concern at this site is the apparent lack of recruitment of new plants of Aloe argentifolia, as all the plants observed in 2013 were mature individuals (McCoy et al. 2017). There is no obvious cause for this lack of seedling recruitment and in view of the natural protection at the site from the waterfalls and rapids, grazing by animals would not seem to be a contributing factor. A key initial conservation action would therefore be to conduct a more thorough population survey at the site and to establish the causes of the recruitment issues.

As noted above, the waterfalls are a natural beauty spot and so have some potential as an ecotourism destination, but at present this is limited due to its isolation from the main tourist destinations in northern Mozambique. The Lúrio River is a major source of fresh water for people living within its catchment.

Iain Darbyshire, Royal Botanic Gardens, Kew

Jo Osborne, Royal Botanic Gardens, Kew